JP2020190221A - Abnormality diagnosis device of reduction catalyst - Google Patents

Abstract

To avoid an erroneous diagnosis of a reduction catalyst.SOLUTION: An abnormality diagnosis device 10 comprises: an SCR 5; an addition valve 6; a NOx sensor 14 for acquiring an upstream-side NOx amount; an addition amount acquisition part 22 for acquiring an addition amount of urea water on the basis of the upstream-side NOx amount; an NH3 sensor 15 for detecting an actual measurement slip amount of a NOx3 amount at a downstream side of the SCR 5; a virtual slip amount calculation part 23 for calculating a virtual slip amount being a virtual value of an NH3 amount at the downstream side of the SCR 5 by using a physical model of the SCR 5; and a diagnosis part 24 for diagnosing the presence or absence of an abnormality of the SCR 5 on the basis of the actual measurement slip amount and the virtual slip amount. The virtual slip amount calculation part 23 calculates a first virtual slip amount being the virtual slip amount by using a first model being a physical model which is set as a delayed rising type rather than the case that the physical model equivalent to an abnormal state of the SCR 5 in terms of a layout is used. When the first virtual slip amount is equal to an allowable threshold or larger, the diagnosis part 24 performs a diagnosis.SELECTED DRAWING: Figure 2

Description

The present invention relates to an abnormality diagnostic device for a reduction catalyst.

As a conventional reduction catalyst abnormality diagnostic device, for example, the technique described in Patent Document 1 is known. In the technique described in Patent Document 1, the estimated adsorbed NH ₃ amount of the reduction catalyst based on the NOx amount contained in the exhaust gas upstream of the reduction catalyst, when the NH3 adsorption amount is specified amount or more, the abnormality diagnosis The process is executed.

Japanese Patent No. 6087866

In the art, it focuses on the actual slip amount is a measured value of the NOx amount or NH ₃ amount contained in the downstream of the exhaust gas of the reduction catalyst, there is a case where the diagnosis of abnormality of the reduction catalyst. When diagnosing such an abnormality of the reduction catalyst, in order to avoid erroneous diagnosis of the abnormality of the reduction catalyst, for example, the reduction catalyst uses a virtual slip amount calculated using a physical model of the reduction catalyst. It is desirable to appropriately estimate that the measured slip amount has increased to the extent that an abnormality can be diagnosed.

An object of the present invention is to avoid erroneous diagnosis of an abnormality of the reduction catalyst.

The reduction catalyst abnormality diagnostic apparatus according to one aspect of the present invention includes a reduction catalyst provided in the exhaust passage of the internal combustion engine, an addition valve provided upstream of the reduction catalyst and adding urea water, and upstream of the reduction catalyst. An upstream NOx amount acquisition unit that acquires the upstream NOx amount, which is the amount of NOx contained in the exhaust gas, an addition amount acquisition unit that acquires the addition amount of urea water based on the upstream NOx amount, and an exhaust gas downstream of the reduction catalyst. the measured slip amount detecting section for detecting the actual slip amount is a measured value of the NOx amount or NH ₃ amount contained in, using a physical model of the reduction catalyst that receives at least the upstream NOx amount and the amount, of the reduction catalyst a virtual slip amount calculating unit that calculates a virtual slip amount is a virtual value of the NOx amount or NH ₃ amount contained in the downstream of the exhaust gas, based on the virtual slip amount and the measured slip amount, the abnormality presence or absence of the reduction catalyst A diagnostic unit that performs diagnosis and a virtual slip amount calculation unit are provided by using the first model, which is a physical model that is a delayed rise type compared to the case where a physical model that corresponds to the abnormal state of the reduction catalyst by design is used. , The first virtual slip amount, which is a virtual slip amount for determining whether or not the diagnosis can be executed by the diagnosis unit, is calculated, and the diagnosis unit executes the diagnosis when the first virtual slip amount is equal to or more than a predetermined permission threshold. To do.

In the reduction catalyst abnormality diagnostic apparatus according to one aspect of the present invention, the diagnosis unit executes the diagnosis when the first virtual slip amount is equal to or higher than a predetermined permission threshold value. The first virtual slip amount is calculated by using the first model, which is a physical model that is a delayed rising type, as compared with the case where a physical model corresponding to the abnormal state of the reduction catalyst is used by design. Therefore, for example, when the measured slip amount rises in an abnormal state of the reduction catalyst, if the first virtual slip amount for determining whether or not the diagnosis can be executed is equal to or more than a predetermined permission threshold value, the reduction catalyst is diagnosed as abnormal. It can be assumed that the measured slip amount has already increased to the extent that it can be obtained. As a result, it is possible to avoid erroneous diagnosis of the abnormality of the reduction catalyst.

In one embodiment, the first model has a higher peak and a smaller full width at half maximum than when a physical model corresponding to the abnormal state of the reduction catalyst is used in comparing the impulse response waveforms of the virtual slip amount for the same input. It may be a physical model that produces an impulse response waveform. In this case, the rise of the first virtual slip amount is slower than when the physical model corresponding to the abnormal state of the reduction catalyst is used by design, and the peak characteristic is sharp so that the peak after the rise is delayed. be able to. Therefore, a first model suitable for the delayed rising type can be used.

In one embodiment, the first model may be a physical model having a larger number of catalyst stages than a physical model that corresponds in design to the abnormal state of the reduction catalyst. In this case, the rise of the first virtual slip amount can be delayed according to the increase in the number of catalyst stages.

In one embodiment, the first model may be a physical model in which the slip speed of the virtual slip amount is larger than the physical model that corresponds in design to the abnormal state of the reduction catalyst. In this case, it becomes easy to increase the first virtual slip amount after the delayed rise according to the increase in the slip speed of the virtual slip amount.

In one embodiment, the virtual slip amount calculation unit makes a diagnosis by the diagnostic unit using a second model, which is a physical model that rises earlier than when a physical model that corresponds to the normal state of the reduction catalyst in design is used. The second virtual slip amount, which is the virtual slip amount for suspending, is calculated, and the diagnostic unit determines that the first virtual slip amount is equal to or greater than the permission threshold and the second virtual slip amount is equal to or greater than the predetermined stop threshold. If this is the case, the diagnosis may be temporarily stopped. In this case, when the second virtual slip amount is equal to or greater than a predetermined stop threshold value, the diagnosis unit temporarily stops the diagnosis. The second virtual slip amount is calculated by using a second model, which is a physical model that rises earlier than when a physical model that corresponds to the normal state of the reduction catalyst in design is used. Therefore, for example, when the actually measured slip amount occurs even in the normal state of the reduction catalyst, if the second virtual slip amount for suspending the diagnosis is equal to or more than the predetermined stop threshold value, the first virtual slip amount is permitted. Even if it is equal to or higher than the threshold value, the diagnosis can be temporarily stopped because the increase in the measured slip amount is not due to an abnormality in the reduction catalyst. As a result, it is possible to avoid erroneous diagnosis of the abnormality of the reduction catalyst more accurately.

According to the present invention, it is possible to avoid erroneous diagnosis of an abnormality of the reduction catalyst.

It is a schematic block diagram which shows the abnormality diagnosis apparatus of the reduction catalyst which concerns on embodiment. It is a block diagram of the structure about the ECU of FIG. It is a diagram illustrating a setting example of the NH ₃ slip speed of the physical model. It is a timing chart which illustrates the 1st virtual slip amount. It is a timing chart which illustrates the 2nd virtual slip amount. It is a flowchart which illustrates the reduction catalyst diagnosis process by the ECU of FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or equivalent elements are designated by the same reference numerals, and duplicate description will be omitted.

[Configuration of reduction catalyst abnormality diagnostic device]
FIG. 1 is a schematic configuration diagram showing an abnormality diagnosis device for a reduction catalyst according to an embodiment. In FIG. 1, the reduction catalyst abnormality diagnosis device 10 is a device provided in the diesel engine (internal combustion engine) 1 for diagnosing the presence or absence of an abnormality in the reduction catalyst, and is mounted on, for example, a vehicle. The diesel engine 1 has an intake passage 2, an exhaust passage 3, and an injector (not shown) that injects fuel into a combustion chamber. In the diesel engine 1, the exhaust gas discharged from the diesel engine 1 is purified by each catalyst provided in the exhaust passage 3.

The reduction catalyst abnormality diagnosis device 10 includes a diesel exhaust particulate filter (particulate filter) [DPF: Diesel Particulate Filter] 4 and a selective reduction catalyst [SCR: Selective Catalytic Reduction] (reduction catalyst) provided in the exhaust passage 3 as catalysts. ) 5 and. The DPF 4 is provided upstream of the SCR 5 in the exhaust passage 3. DPF4 removes PM from the exhaust gas by collecting particulate matter [PM: Particulate Matter] contained in the exhaust gas. SCR5 reduces and purifies NOx contained in the exhaust gas.

The reduction catalyst abnormality diagnosis device 10 includes an addition valve 6 arranged on the upstream side of the SCR 5 in the exhaust passage 3, specifically, in the exhaust passage 3 between the DPF 4 and the SCR 5. The addition valve 6 is connected to the urea water tank via a supply pipe (not shown), and adds urea water to the SCR5. When urea water is added to SCR 5 by the addition valve 6, the urea water becomes NH ₃ and is adsorbed on SCR 5, and the NH ₃ reacts with NOx in the exhaust gas to reduce NOx.

There is an upper limit to the amount of NH _{3 that} can be adsorbed on SCR5. For example, if an excessive amount of NH ₃ is supplied to the SCR 5 with respect to the upper limit, the NH ₃ not adsorbed by the SCR ₅ may flow out (slip) from the SCR 5.

The SCR5 has a normal state and an abnormal state with respect to the purification performance and the adsorption performance of the SCR5. The normal state of SCR5 means, for example, a state in which the purification performance and adsorption performance of SCR5 are maintained to such an extent that the NOx concentration on the downstream side of SCR5 satisfies the exhaust gas regulation by law. The abnormal state of SCR5 means, for example, a state in which the purification performance and adsorption performance of SCR5 have deteriorated to some extent that the NOx concentration on the downstream side of SCR5 may not satisfy the exhaust gas regulation by law. In the abnormal state of SCR5, the amount of NH ₃ that can be adsorbed decreases and the slip amount of NH ₃ tends to increase as compared with the normal state of SCR5.

FIG. 2 is a block diagram of the configuration of the ECU of FIG. As shown in FIGS. 1 and 2, the reduction catalyst abnormality diagnosis device 10 includes an intake amount sensor 11, an engine state sensor 12, an exhaust temperature sensor 13, a NOx sensor (upstream NOx amount acquisition unit) 14, and It is equipped with an NH ₃ sensor (measured slip amount detection unit) 15 and an ECU [Electronic Control Unit] 20. The sensors 11 to 15 and the addition valve 6 are connected to the ECU 20.

The intake air amount sensor 11 is, for example, a detector provided in the intake air passage 2 of the diesel engine 1 and detecting the intake air amount of the diesel engine 1. The intake air amount sensor 11 transmits a detection signal of the detected intake air amount to the ECU 20.

The engine state sensor 12 is a sensor for acquiring the engine state. The engine state sensor 12 is, for example, a detector that detects the rotation speed of the diesel engine 1 (hereinafter referred to as the engine rotation speed), the load of the diesel engine 1, and the like. The engine state sensor 12 transmits a detection signal regarding the detected engine state to the ECU 20.

The exhaust temperature sensor 13 is a detector that detects the temperature (inlet temperature) of the exhaust gas between the DPF 4 and the SCR 5 in the exhaust passage 3 as the exhaust temperature. The exhaust temperature sensor 13 transmits the detected exhaust temperature detection signal to the ECU 20.

The NOx sensor 14 is a detector that detects the upstream NOx concentration of the exhaust gas between the DPF 4 and the SCR 5 in the exhaust passage 3. The upstream NOx concentration is the NOx concentration (NOx amount) contained in the exhaust gas upstream of the SCR5. The NOx sensor 14 transmits a detection signal of the detected upstream NOx concentration to the ECU 20.

The NH ₃ sensor 15 is a detector that detects the NH ₃ concentration of the exhaust gas downstream of the SCR 5 in the exhaust passage 3. The NH ₃ concentration here is an actually measured slip amount which is an actually measured value of the NH ₃ concentration (NH ₃ amount) contained in the exhaust gas downstream of the SCR5. The NH ₃ sensor 15 transmits a detection signal of the detected actual slip amount to the ECU 20.

The ECU 20 is an electronic control unit having a CPU [Central Processing Unit], a ROM [Read Only Memory], a RAM [Random Access Memory], a CAN [Controller Area Network] communication circuit, and the like. In the ECU 20, various functions are realized by loading the program stored in the ROM into the RAM and executing the program loaded in the RAM in the CPU. The ECU 20 may be composed of a plurality of electronic control units.

The ECU 20 has an engine state acquisition unit 21, an addition amount acquisition unit 22, a virtual slip amount calculation unit 23, and a diagnosis unit 24 as functional configurations.

The engine state acquisition unit 21 acquires various engine states based on the detection signals of the intake air amount sensor 11, the engine state sensor 12, the exhaust temperature sensor 13, the NOx sensor 14, and the NH ₃ sensor 15.

The engine state acquisition unit 21 acquires the exhaust temperature between the DPF 4 and the SCR 5 in the exhaust passage 3 as the temperature of the SCR 5 based on the detection signal of the exhaust temperature sensor 13. Alternatively, the engine state acquisition unit 21 may calculate the fuel injection amount from the engine speed and the load, and acquire the estimated temperature of the SCR 5 from the fuel injection amount and the intake air amount. In this case, the exhaust temperature sensor 13 may be omitted.

The engine state acquisition unit 21 acquires the upstream NOx concentration based on the detection signal of the NOx sensor 14. Alternatively, the engine state acquisition unit 21 may calculate the fuel injection amount from the engine rotation speed and the load, and acquire the estimated value of the upstream NOx concentration from the fuel injection amount and the intake air amount as the engine state. In this case, the engine state acquisition unit 21 may function as the upstream NOx amount acquisition unit, and the NOx sensor 14 may be omitted.

The engine state acquisition unit 21 acquires the measured slip amount of NH ₃ based on the detection signal of the NH ₃ sensor 15. The measured slip amount of NH ₃ is used for diagnosing the presence or absence of an abnormality in SCR 5, which will be described later.

The addition amount acquisition unit 22 acquires the addition amount of urea water by the addition valve 6 based on the upstream NOx concentration. The addition amount acquisition unit 22 acquires, for example, the addition amount of urea water necessary for purifying NOx contained in the exhaust gas upstream of the SCR5 according to the acquired upstream NOx concentration or the estimated upstream NOx concentration. The addition amount acquisition unit 22 may acquire a preset addition amount of urea water necessary for maintaining the NH ₃ adsorption amount with respect to SCR5. The amount of addition may be, for example, an amount corresponding to the amount of NH ₃ required to purify all NOx having a NOx concentration detected by the NOx sensor 14. The addition amount acquisition unit 22 causes the addition valve 6 to add urea water at a predetermined addition timing based on the acquired urea water addition amount.

Virtual slip amount calculating section 23, at least the upstream NOx amount and the amount using SCR5 of the physical model to the input, the virtual value of the amount NH ₃ contained in the downstream of the exhaust gas SCR5 (here NH ₃ concentration) Calculate a certain virtual slip amount. The virtual slip amount calculation unit 23 receives, for example, the upstream NOx amount, the addition amount, and the temperature of the SCR5 as inputs according to a known calculation method using the physical model of the SCR5, and the NH ₃ associated with the NOx reduction reaction in the SCR5. The virtual adsorption amount and virtual slip amount of NH ₃ are calculated from the balance and the upper limit value of the NH ₃ adsorption amount in SCR5. The virtual adsorption amount and virtual slip amount of NH ₃ here are different from the physical model conforming to the general design specifications of SCR5 in order to determine, for example, whether or not the diagnosis can be performed by the diagnosis unit 24 described later. By using a physical model, it is calculated by intentionally making it different from the approximate values of the actual adsorption amount and slip amount of NH ₃ .

The physical model according to the design specifications of the SCR5 means a physical model of the SCR5 in which the parameters in the model design are determined so as to show the same characteristics as the characteristics of the actual SCR5. The characteristics of SCR5, for example, for the amount of a constant change in the case where the temperature of the upstream NOx amount and SCR5 constant as the input (hereinafter, simply referred to as "amount-varying input"), the rise of the NH ₃ slip response And the peak after the rise is mentioned.

Examples of the physical model conforming to the design specifications of the SCR 5 include a physical model that corresponds to the normal state of the SCR 5 by design and a physical model that corresponds to the abnormal state of the SCR 5 by design. The physical model that corresponds to the normal state of SCR5 by design is the same as the characteristics of the actual SCR5, for example, in a new state or a state that is in the category of normal deterioration by law (for example, a deteriorated product equivalent to running 4 km or 120 km). It means a physical model of SCR5 in which parameters for model design are determined so as to show characteristics. The physical model that corresponds to the abnormal state of SCR5 by design is a model design parameter that shows the same characteristics as the actual SCR5 whose abnormal state is created by, for example, deterioration acceleration endurance operation at the failure level. It means the determined physical model of SCR5.

The virtual slip amount calculation unit 23 uses the first model as the physical model of the SCR5, inputs the upstream NOx amount, the addition amount, and the temperature of the SCR5, and determines whether or not the diagnosis can be executed by the diagnosis unit 24. The first virtual slip amount, which is an amount, is calculated.

The first model is a physical model that is a delayed rising type as compared with the case where a physical model corresponding to the abnormal state of SCR5 is used by design. In the delayed rising type, the first virtual slip amount is added in the same amount as the virtual slip amount in the physical model (hereinafter, simply referred to as "abnormal virtual slip amount") corresponding to the abnormal state of SCR5 by design. It means the characteristic of the rise response such that the rise is delayed with respect to the amount change input. In the first model, in addition to the delayed rising type, the sharp peak in which the first virtual slip amount rises later than the abnormal virtual slip amount with respect to the same addition amount change input is higher. It may be a characteristic physical model.

As an example, in the comparison of the impulse response waveforms of the virtual slip amount for the same addition amount change input, the first model has a higher peak and a smaller half width than the case of using a physical model corresponding to the abnormal state of SCR5 by design. It may be a physical model that produces an impulse response waveform.

In order to obtain such characteristics, specifically, the first model may be a physical model having a larger number of catalyst stages than a physical model that corresponds to the abnormal state of SCR5 by design. For example, when the number of catalyst stages in the physical model corresponding to the abnormal state of SCR5 in design is one, the number of catalyst stages in the first model can be, for example, two. The number of catalyst stages in the first model may be two or more.

Specifically, the first model may be a physical model in which the NH ₃ slip speed (slip speed of the virtual slip amount) is larger than the physical model that corresponds to the abnormal state of SCR5 in design. FIG. 3 is a diagram showing a setting example of the NH ₃ slip speed of the physical model. As shown in FIG. 3, when the temperature of SCR5 is constant and compared, the larger the amount of NH ₃ adsorbed, the higher the NH ₃ slip velocity. In FIG. 3, when the NH ₃ slip velocity of the physical model corresponding to the abnormal state of SCR5 by design is represented by, for example, the curve L1, the NH ₃ slip velocity of the first model is represented by the curve L2. You may. The NH ₃ slip speed of the first model may be approximately twice the NH ₃ slip speed of the physical model corresponding to the abnormal state of SCR5 by design. When the number of catalyst stages of the first model is two or more, the NH ₃ slip speed of the first model is more than twice the NH ₃ slip speed of the physical model corresponding to the abnormal state of SCR5 by design. You may.

FIG. 4 is a timing chart illustrating the first virtual slip amount. In FIG. 4, the first virtual slip amount SL ₁ is shown by a solid line and the abnormal virtual slip amount SL _MAL is shown by a broken line for the same addition amount change input. As shown in FIG. 4, by using the first model, the waveform of the first virtual slip amount SL ₁ is sharpened in addition to the delayed rising type as described above, as compared with the abnormal virtual slip amount SL _MAL. It can be a characteristic. Therefore, for example, the permission threshold TH ₁ , which is the threshold of the first virtual slip amount SL ₁ for determining whether or not the diagnosis can be executed, is set to the first virtual slip amount of the sharp peak portion in which the first virtual slip amount SL ₁ is increased. By appropriately setting the value of SL ₁ , for example, when the measured slip amount rises in the abnormal state of the actual SCR 5, if the first virtual slip amount SL ₁ is equal to or higher than the permission threshold TH ₁ , the SCR 5 is regarded as abnormal. It can be assumed that the measured slip amount has already increased to the extent that it can be diagnosed.

The virtual slip amount calculation unit 23 uses the second model as the physical model of the SCR5, and inputs the upstream NOx amount, the addition amount, and the temperature of the SCR5 as the virtual slip amount for suspending the diagnosis by the diagnosis unit 24. A certain second virtual slip amount is calculated.

The second model is a physical model that rises earlier than when a physical model that corresponds to the normal state of SCR5 by design is used. In the early rise type, the second virtual slip amount is added in the same amount as the virtual slip amount in the physical model (hereinafter, simply referred to as "normal virtual slip amount") corresponding to the normal state of SCR5 by design. It means the characteristic of the rise response that rises early in response to the quantity change input. In the second model, in addition to the early rise type, the second virtual slip amount is broader than the normal virtual slip amount so that the peak after early rise is low and gentle with respect to the same addition amount change input. It may be a physical model with various peak characteristics.

As an example, in the comparison of the impulse response waveforms of the virtual slip amount for the same addition amount change input, the second model has a lower peak and a larger half-value width than the case of using the physical model corresponding to the normal state of SCR5 by design. It may be a physical model that produces an impulse response waveform.

In order to obtain such characteristics, specifically, the second model is a physical model having the same number of catalyst stages as the physical model that corresponds to the normal state of SCR5 by design, and corresponds to the normal state of SCR5 by design. than the physical model may be NH ₃ physical slip speed is smaller models. For example, as shown in FIG. 3, when the NH ₃ slip velocity of the physical model corresponding to the normal state of SCR5 by design is represented by, for example, the curve L3, the NH ₃ slip velocity of the second model is represented by the curve L4. It may be represented. The NH ₃ slip speed of the second model may be approximately half the NH ₃ slip speed of the physical model that corresponds in design to the normal state of SCR5. As described above, in the abnormal state of SCR5, the amount of NH ₃ that can be adsorbed decreases and the slip amount of NH ₃ tends to increase as compared with the normal state of SCR5. Therefore, the NH of the first model _{The characteristics of the 3-} slip speed and the NH _3- slip speed of the second model are different from each other. More specifically, when the temperature of SCR5 is constant and compared, the NH ₃ slip velocity of the first model represented by the curve L1 is larger than the NH ₃ slip velocity of the second model represented by the curve L3. It has become.

FIG. 5 is a timing chart illustrating the second virtual slip amount. In FIG. 5, the second virtual slip amount SL ₂ is shown by a solid line and the normal virtual slip amount SL _NRM is shown by a broken line for the same addition amount change input. As shown in FIG. 5, by using the second model, the waveform of the second virtual slip amount SL ₂ is increased to the broad peak in addition to the early rising type as described above, as compared with the normal virtual slip amount SL _NRM. It can be a characteristic. Thus, for example, the stop threshold value TH ₂ second is the threshold of a virtual slip amount SL ₂ for temporarily stopping the diagnosis, the second virtual slip amount SL ₂ of broad peaks at a position where the second virtual slip amount SL ₂ is increased By appropriately setting the value of, for example, if the second virtual slip amount SL ₂ is equal to or higher than the stop threshold TH ₂ when the measured slip amount occurs even in the normal state of SCR5, the first virtual slip amount SL ₁ Even if the permission threshold is TH ₁ or higher, the increase in the measured slip amount is not an increase due to an abnormality in SCR5 (that is, it is not abnormal because slip occurs even in a normal SCR5), and the diagnosis is temporarily stopped. can do.

The diagnosis unit 24 diagnoses the presence or absence of an abnormality in SCR5 based on the measured slip amount and the virtual slip amount. For example, when the first virtual slip amount SL ₁ is equal to or higher than the above-mentioned permission threshold TH ₁ , the diagnosis unit 24 diagnoses the presence or absence of an abnormality in the SCR 5. For example, when the first virtual slip amount SL ₁ is equal to or higher than the permission threshold TH ₁ and the second virtual slip amount SL ₂ is equal to or higher than the stop threshold TH ₂ described above, the diagnostic unit 24 determines that the SCR 5 is abnormal. The presence or absence diagnosis may be temporarily stopped.

When the diagnosis unit 24 executes the diagnosis of the presence or absence of abnormality in SCR5 (for example, the first virtual slip amount SL ₁ is equal to or higher than the permission threshold TH ₁ and the second virtual slip amount SL ₂ is the stop threshold value described above. (When TH _{2 or} less), the measured slip amount of NH ₃ is compared with a predetermined abnormality determination threshold value, and for example, when the measured slip amount is equal to or more than the abnormality determination threshold value, SCR 5 is diagnosed as abnormal. The diagnosis unit 24 may diagnose the SCR5 as abnormal when executing the diagnosis of the presence or absence of the abnormality of the SCR5, for example, when the measured slip amount is equal to or more than the abnormality determination threshold value for a certain period of time.

[Processing by ECU]
Next, an example of processing by the ECU 20 will be described with reference to FIG. FIG. 6 is a flowchart illustrating the reduction catalyst diagnosis process by the ECU 20. The ECU 20 of the reduction catalyst abnormality diagnosis device 10 repeatedly executes the reduction catalyst diagnosis process shown in FIG. 6 during operation under certain conditions (for example, while the vehicle is running) such as after warming up the diesel engine 1.

As shown in FIG. 6, the ECU 20 acquires the upstream NOx concentration by the engine state acquisition unit 21 in S01. In S02, the ECU 20 acquires the addition amount of urea water by the addition valve 6 by the addition amount acquisition unit 22. The ECU 20 detects the measured slip amount of NH ₃ by the NH ₃ sensor 15 in S03.

In S04, the ECU 20 calculates the first virtual slip amount SL ₁ by using the virtual slip amount calculation unit 23 using the first model. In S05, the ECU 20 determines whether or not the first virtual slip amount SL ₁ is equal to or higher than the permission threshold TH ₁ by the diagnosis unit 24.

When the diagnosis unit 24 determines that the first virtual slip amount SL ₁ is equal to or higher than the permission threshold TH ₁ (S05: YES), the ECU 20 uses the second model by the virtual slip amount calculation unit 23 in S06. The second virtual slip amount SL ₂ is calculated. In S07, the ECU ₂₀ determines whether or not the second virtual slip amount SL ₂ is less than the stop threshold TH ₂ by the diagnosis unit 24. When the diagnosis unit 24 determines that the second virtual slip amount SL ₂ is less than the stop threshold value TH ₂ (S07: YES), the ECU 20 executes a diagnosis of the presence or absence of an abnormality in the SCR 5 in S08. After that, the ECU 20 ends the process shown in FIG.

On the other hand, when the diagnosis unit 24 determines that the first virtual slip amount SL ₁ is less than the permission threshold TH ₁ (S05: NO), the ECU 20 executes the diagnosis of the presence or absence of the abnormality of the SCR 5 by the diagnosis unit 24. No, the process of FIG. 6 ends.

Further, when the diagnosis unit 24 determines that the first virtual slip amount SL ₁ is equal to or higher than the permission threshold TH ₁ , the diagnosis unit 24 determines that the second virtual slip amount SL ₂ is equal to or higher than the stop threshold TH _2. If this is the case (S05: YES and S07: NO), the ECU 20 temporarily stops the diagnosis of the presence or absence of the abnormality of the SCR 5 by the diagnosis unit 24, and ends the process of FIG.

[Action and effect]
As described above, in the reduction catalyst abnormality diagnosis device 10, when the first virtual slip amount SL ₁ is equal to or higher than the predetermined permission threshold TH ₁ , the diagnosis unit 24 executes the diagnosis. The first virtual slip amount SL ₁ is calculated by using the first model, which is a physical model that is a delayed rising type, as compared with the case where the physical model corresponding to the abnormal state of the SCR ₅ is used by design. Thus, for example, when the actual slip amount rises in an abnormal state of SCR5, if the first virtual slip amount SL ₁ for determining executability of diagnosis becomes permitted threshold TH ₁ or more, SCR5 is diagnosed as abnormal It can be assumed that the measured slip amount has already increased to the extent that it can be obtained. As a result, it is possible to avoid erroneous diagnosis of the abnormality of SCR5.

In the reduction catalyst abnormality diagnostic apparatus 10, the first model has a peak in comparison of the impulse response waveforms of the virtual slip amount for the same addition amount change input as compared with the case of using the physical model corresponding to the abnormal state of SCR5 by design. It is a physical model that produces an impulse response waveform that is high and has a small half-value width. As a result, the rise of the first virtual slip amount SL ₁ is slower than when a physical model corresponding to the abnormal state of SCR 5 is used by design, and the peak characteristic after the rise is delayed is sharpened. can do. Therefore, a first model suitable for the delayed rising type can be used.

In the reduction catalyst abnormality diagnostic apparatus 10, the first model is a physical model having a larger number of catalyst stages than the physical model that corresponds to the abnormal state of the SCR 5 in design. As a result, the rise of the first virtual slip amount SL ₁ can be delayed according to the increase in the number of catalyst stages.

In the abnormality diagnostic device 10 of the reduction catalyst, the first model, than the physical model corresponding to the design to the abnormal state of SCR5, NH ₃ slip speed is greater physical model. As a result, it becomes easy to increase the first virtual slip amount SL ₁ after the delayed rise according to the increase in the NH ₃ slip speed.

In the reduction catalyst abnormality diagnosis device 10, the virtual slip amount calculation unit 23 uses the second model, which is a physical model that rises earlier than the case where the physical model corresponding to the normal state of the SCR 5 in design is used. The second virtual slip amount SL ₂ , which is the virtual slip amount for suspending the diagnosis by the diagnosis unit 24, is calculated, and the diagnosis unit 24 calculates the first virtual slip amount SL _{1 of which} is equal to or higher than the permission threshold TH _1. , When the second virtual slip amount SL ₂ is equal to or higher than the stop threshold TH ₂ , the diagnosis is temporarily stopped. As a result, when the second virtual slip amount SL ₂ is equal to or higher than the stop threshold value TH ₂ , the diagnosis unit 24 temporarily stops the diagnosis. The second virtual slip amount SL ₂ is calculated by using a second model, which is a physical model that rises earlier than when a physical model that corresponds to the normal state of SCR 5 by design is used. Therefore, for example, when the measured slip amount occurs even in the normal state of SCR5, if the second virtual slip amount SL ₂ for suspending the diagnosis is equal to or higher than the stop threshold TH ₂ , the first virtual slip amount SL _{Even if 1} is equal to or higher than the permission threshold TH ₁ , the diagnosis can be temporarily stopped because the increase in the measured slip amount is not an increase due to an abnormality in SCR5. As a result, it is possible to avoid the false diagnosis of the abnormality of SCR5 more accurately.

[Modification example]
Although the embodiments according to the present invention have been described above, the present invention is not limited to the above-described embodiments.

In the above embodiment, the first model, than the physical model corresponding to the design to the abnormal state of SCR5, is a catalyst stages many physical model, although NH ₃ slip speed is greater physical model, but not limited to .. Further, in the comparison of the impulse response waveforms of the virtual slip amount for the same addition amount change input, the first model has an impulse with a higher peak and a smaller half-value width than when a physical model corresponding to the abnormal state of SCR5 is used. The physical model was such that it became a response waveform, but it is not limited to this. In short, if the first model is a physical model that is delayed rising compared to the case where the physical model corresponding to the abnormal state of SCR5 is used by design, a physical model parameter setting different from the above is used. It may be used as the first model.

In the above embodiment, the upstream NOx concentration is exemplified as the NOx amount, but the NOx amount may be various physical quantities such as the mass flow rate and mass of NOx contained in the exhaust gas upstream of the SCR5.

The above embodiment has exemplified the NH ₃ concentration as NH ₃ amount, NH ₃ amount is the mass flow rate of the NH ₃ contained in the downstream of the exhaust gas SCR5, mass or the like, may be of various physical quantities.

In the above embodiment, the actual slip amount and the virtual slip has been described by way of measured values and the virtual value of the amount of NH ₃ contained in the downstream of the exhaust gas SCR5, measured slip amount and the virtual amount of slip, the downstream SCR5 It may be an actually measured value or a virtual value of the amount of NOx contained in the exhaust gas. That is, the presence or absence of an abnormality in SCR5 may be diagnosed by paying attention to the amount of NOx slip from SCR5. In this case, the measured slip amount detecting unit may be, for example, a NOx sensor that detects the measured value of the NOx amount contained in the exhaust gas downstream of the SCR5, instead of the NH ₃ sensor 15. Virtual slip amount calculation section 23, instead of the virtual slip amount of NH _3, at least the upstream NOx amount and the amount using SCR5 physical model as input, virtual NOx amount contained in the downstream of the exhaust gas SCR5 The value (virtual slip amount of NOx) may be calculated. Further, the diagnosis unit 24 may diagnose the presence or absence of an abnormality in SCR5 based on, for example, the measured slip amount of NOx instead of the measured slip amount of NH ₃ .

The diagnosis unit 24 temporarily stopped the diagnosis when the first virtual slip amount was equal to or higher than the permission threshold value and the second virtual slip amount was equal to or higher than the stop threshold value. For example, the first virtual slip amount was temporarily stopped. However, if the second virtual slip amount is equal to or greater than the stop threshold value, the diagnosis may not be executed. In this case, the processing of S06 and S07 in FIG. 6 may be performed between S04 and S05.

The virtual slip amount calculation unit 23 does not necessarily have to calculate the second virtual slip amount using the second model. The diagnosis unit 24 does not necessarily have to temporarily stop the diagnosis when the first virtual slip amount is equal to or more than the permission threshold value and the second virtual slip amount is equal to or more than the stop threshold value.

In the above embodiment, the diesel engine 1 of a 4-cylinder in-line engine is exemplified as the internal combustion engine, but the internal combustion engine is not limited to this.

3 ... Exhaust passage, 5 ... SCR (selective reduction catalyst, reduction catalyst), 6 ... Addition valve, 10 ... Reduction catalyst abnormality diagnostic device, 14 ... NOx sensor (upstream NOx amount acquisition unit), 15 ... NH ₃ sensor (actual measurement) Slip amount detection unit), 22 ... Addition amount acquisition unit, 23 ... Virtual slip amount calculation unit, 24 ... Diagnosis unit.

Claims (5)

The reduction catalyst provided in the exhaust passage of the internal combustion engine and
An addition valve provided upstream of the reduction catalyst to add urea water,
An upstream NOx amount acquisition unit that acquires an upstream NOx amount, which is the amount of NOx contained in the exhaust gas upstream of the reduction catalyst,
An addition amount acquisition unit that acquires the addition amount of the urea water based on the upstream NOx amount,
Wherein the measured slip amount detecting section for detecting the actual slip amount is a measured value of the NOx amount or NH ₃ amount contained in the downstream of the exhaust gas of the reduction catalyst,
At least using the physical model of the reduction catalyst that receives the upstream NOx amount and the amount, calculated virtual slip amount is a virtual value of the NOx amount or NH ₃ amount contained in the exhaust gas downstream of the reduction catalyst Virtual slip amount calculation unit and
A diagnostic unit that diagnoses the presence or absence of an abnormality in the reduction catalyst based on the measured slip amount and the virtual slip amount.
With
The virtual slip amount calculation unit is described by the diagnostic unit using the first model, which is the physical model that is delayed from the case of using the physical model that corresponds to the abnormal state of the reduction catalyst in design. The first virtual slip amount, which is the virtual slip amount for determining whether or not the diagnosis can be executed, is calculated.
The diagnosis unit is an abnormality diagnosis device for a reduction catalyst that executes the diagnosis when the first virtual slip amount is equal to or higher than a predetermined permission threshold value. In the comparison of the impulse response waveforms of the virtual slip amount with respect to the same input, the first model has a higher peak and a smaller half-value width than the case of using the physical model corresponding to the abnormal state of the reduction catalyst by design. The abnormality diagnostic apparatus for a reduction catalyst according to claim 1, which is the physical model that produces the impulse response waveform. The abnormality diagnostic apparatus for a reduction catalyst according to claim 1 or 2, wherein the number of catalyst stages of the first model is larger than that of the physical model corresponding to the abnormal state of the reduction catalyst in design. The abnormality diagnostic apparatus for a reduction catalyst according to claim 3, wherein the slip speed of the virtual slip amount of the first model is larger than that of the physical model which corresponds to the abnormality state of the reduction catalyst in design. The virtual slip amount calculation unit uses a second model, which is a physical model that rises earlier than the case where the physical model corresponding to the normal state of the reduction catalyst in design is used, and is described by the diagnostic unit. The second virtual slip amount, which is the virtual slip amount for suspending the diagnosis, is calculated.
The diagnosis unit temporarily stops the diagnosis when the first virtual slip amount is equal to or higher than the permission threshold value and the second virtual slip amount is equal to or higher than a predetermined stop threshold value. The abnormality diagnostic apparatus for a reduction catalyst according to any one of 1 to 4.

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